Question: Determine how many solutions exist for the system of equations. ${-x+y = -9}$ ${x+y = 6}$
Convert both equations to slope-intercept form: ${-x+y = -9}$ $-x{+x} + y = -9{+x}$ $y = -9+x$ ${y = x-9}$ ${x+y = 6}$ $x{-x} + y = 6{-x}$ $y = 6-x$ ${y = -x+6}$ Just by looking at both equations in slope-intercept form, what can you determine? ${y = x-9}$ ${y = -x+6}$ The linear equations have different slopes. ${1}$ ${2}$ ${3}$ ${4}$ ${5}$ ${6}$ ${7}$ ${8}$ ${9}$ ${\llap{-}2}$ ${\llap{-}3}$ ${\llap{-}4}$ ${\llap{-}5}$ ${\llap{-}6}$ ${\llap{-}7}$ ${\llap{-}8}$ ${\llap{-}9}$ ${1}$ ${2}$ ${3}$ ${4}$ ${5}$ ${6}$ ${7}$ ${8}$ ${9}$ ${\llap{-}2}$ ${\llap{-}3}$ ${\llap{-}4}$ ${\llap{-}5}$ ${\llap{-}6}$ ${\llap{-}7}$ ${\llap{-}8}$ ${\llap{-}9}$ When two equations have different slopes, the lines will intersect once with one solution.